Try a broker - Adrian Flux is good - but do not go for their monthly payment plan. It is a loan and the APR is horrendous.
Cheaper to use your overdraft or get a 12 month bank loan. The plans they recommend are good - using financially strong companies with good claims paying histories.
If you are happy to deal direct - try NFU - very competitive and the monthly plan costs only a
The May edition of the Caravan Magazine has an article about the Insurers and has rated them all on a star system.If you can get the magazine I am sure you will find it illuminating.
We used to be with NFU but discovered that if there is a claim on the awning.....they will not pay out unless there is damage to the caravan also ( Very strange ).....this is also mentioned in the magazine.